Wireless radio frequency (RF) devices often include integrated circuits (ICs) that operate to receive RF input signals, transmit RF output signals, or both receive and transmit RF signals. Where receive functionality is included, RF communication ICs typically receive analog signals from antennas and convert the analog signals to digital data. Where transmit functionality is included, RF communication ICs typically convert digital data to analog output signals and transmit these analog output signals through power amplifiers to antennas. To increase or maximize power transfer from antennas during receive modes, matching circuits can be used so that the input impedance matches the impedance of the antenna during reception. To increase or maximize power transfer to antennas during transmit modes, matching circuits can also be used so that the output impedance matches the impedance of the antenna during transmit. Configurable matching circuits have been included on-chip to provide this impedance matching.
FIG. 1 (Prior Art) is a circuit diagram of an example embodiment 100 that includes an on-chip matching network 120 that is configurable based upon a variable capacitance 126. The integrated circuit 102 includes a receive mixer 108, a low noise amplifier 116, a frequency synthesizer 110 including a controlled oscillator 112, a transmit mixer 109, a power amplifier 118, and a matching network 120. A harmonic rejection filter 106 is coupled off-chip between the connection pad 132 and an input/output node 103. It is also noted that for some prior solutions, the matching network 120 is also included off-chip, and one off-chip circuit block can be used to provide both a matching function and a harmonic rejection function. The input/output node 103 is coupled to an antenna, which is represented by load 105. One common impedance for an antenna is 50 Ohms, although other antenna impedances can also be used. The integrated circuit 102 includes a receive path and a transmit path.
For the receive path, an RF input signal is received at the antenna or load 105 and is provided to connection pad 132 through the off-chip harmonic rejection filter 106. The receive signal then passes through the matching network 120 and the low noise amplifier 116 before being down-converted to a lower frequency by the receive mixer 108. The receive mixer 108 receives a local-oscillator mixing signal from the on-chip frequency synthesizer 110, which includes the controlled oscillator 112. The down-converted RF input signal 114 is then further processed by circuitry within the integrated circuit 102. For example, the down-converted RF input signal 114 can be converted to digital values by an analog-to-digital converter and then processed by digital processing circuitry within the integrated circuit 102.
For the transmit path, an analog output signal 115 is received by the power amplifier 118 through the transmit mixer 109. This analog output signal 115 can be, for example, an output from a digital-to-analog converter that receives a digital signal generated by digital processing circuitry within the integrated circuit 102. The transmit mixer 109 receives a local-oscillator mixing signal from the on-chip frequency synthesizer 110, which includes the controlled oscillator 112. The transmit mixer 109 up-converts the analog output signal 115 to an RF output signal at a desired transmit frequency. This up-converted RF output signal is provided to power amplifier 118, which can be programmable to generate a transmit output signal at a desired power level. It is also noted that the direct modulation can also be used where the local oscillator signal from frequency synthesizer 110 is modulated with the transmit data and then fed directly into the power amplifier 118. The transmit output signal is passed through the matching network 120 and the connection pad 132 to the harmonic rejection filter 106 before being transmitted through the antenna or load 105.
The configurable matching network 120 can be implemented using a first inductance 122, a second inductance 124, and a variable capacitance 126. The variable capacitance 126 is controlled to provide matching for the input and/or output impedances. For the embodiment depicted, the first inductor (L1) 122 is coupled between node 134 and node 136, and the second inductor (L2) 124 is coupled between node 136 and the pad 132. The variable capacitance (C) 126 is coupled between node 136 and ground 130 and can be controlled, for example, with an on-chip controller. During operation, the configurable matching network 120 is controlled to provide impedance matching. It is noted that U.S. Pat. No. 10,141,971 describes embodiments that provide on-chip configurable matching networks. U.S. Pat. No. 10,141,971 is hereby incorporated by reference in its entirety.
It is noted that filtering can utilize active or passive techniques. For transmit modes, active techniques rely on combining outputs of multiple power amplifiers running at different phases or rely on calibrating a conduction angle for the power amplifier. These active techniques may also use switched-capacitor circuits that create notches at frequencies that are multiples or harmonics of the transmit clock frequency. Active techniques, however, are very sensitive to timing inaccuracies and usually consume relatively high power. Passive techniques use inductors and capacitors to provide harmonic filtering and often use switched techniques. While passive techniques consume less power, passive techniques are not easily tunable because switched passive circuits usually have low quality (Q) factors that degrade maximum achievable filtering. As such, prior solutions have not used on-chip tunable passive techniques to implement harmonic filtering. Rather, off-chip filtering has been used for RF communication devices, such as the harmonic rejection filter 106 shown in FIG. 1 (Prior Art). While the off-chip harmonic rejection filter 106 improves performance of the RF communications, the external components required to implement the harmonic rejection filter 106 increase cost and size requirements for RF communication devices.